Since my system is not the fastest of them all (Wallstreet 233) I'm using a dedicated swap partition as well. To prevent using it in the seldom case of having booted MacOS 9 I use UFS for my swap. UFS partitions do not get mounted under MacOS 9 and are under priviledge control when booted in MacOS X. For the performance concerned I could not notice any difference in speed having the partition using HFS+ or UFS. Not that I have done intensive benchmarking but there's no difference in feel.
Greetings from the monsterjaeger